This invention relates to a stitch density adjusting device of a circular knitting machine for knitting stockings, panty hose, tights and the like.
A conventional circular knitting machine of the above kind comprises a needle cylinder carrying a number of knitting needles in a vertically displaceable manner. In order to enable varying of the density of stitches produced by the knitting machine, there is provided a stitch density adjusting device. For varying the stitch density, a fashioning cam and a stitch density adjusting lever are provided. The fashioning cam acts on an end of the stitch density adjusting lever to cause it to swing vertically about a pivot. There is provided a rising ring below the knitting cylinder. The stitch density adjusting lever acts on the rising ring via an abutment piece as the lever swings vertically, thereby raising and lowering the needle cylinder through the rising ring and rising pins provided between the needle cylinder and the rising ring, whereby the density of stitches of the knitted yarn is changed or adjusted as will be described in more detail hereinafter.
By adjusting the stitch density gradually in the manner as described above, a knitted fabric having a gradually changing circumference is obtained depending upon the contour of the fashioning cam. For example, a panty hose having a gradually decreasing circumference from a welt portion to an ankle portion can be knitted.
With the type of stitch density adjusting device described above, the fashioning cam must be replaced with another fashioning cam in order to knit a product having a gradually increasing circumference or an irregularly changing circumference. Furthermore, it is very difficult to knit a product having an irregularly changing circumference with the conventional stitch density adjusting device using the fashioning cam.
Circular knitting machines of the type described above are operated at high speed and the needle cylinder is rotated, for example, at 200 to 1500 RPM, for the purpose of improving the operating efficiency.
This causes a problem of the needle cylinder and its associated parts are heated up to about 70.degree. to 80.degree. C. due to frictional resistance in continuous operation. As the needle cylinder and the associated parts are subjected to temperature rise, they undergo thermal expansion which is of the order of 0.15 to 0.2 mm in the axial direction of the needle cylinder. The thermal expansion undesirably causes elongation of the knitted products of the order of 10 to 15% of the standard knitted length.